MATERIALS FOR ORTHOPEDIC APPLICATIONS - Advanced Biomaterials: Fundamentals, Processing, and Applications - page 56

following aspects are not covered in any detailed manner: a) synthesis of
hydroxyapatite powders, and b) processing of porous bioactive coatings or
porous bulk biomaterials.
Section 3.2 emphasizes the chemistry and properties of natural hard tissues.
In discussing different materials system and their applications, the discussion
starts with hydroxyapatite based composite biomaterials.
Section 3.3 provides examples of different HAp based composites, which
are well characterized and reported in the existing literature. In addition to the
literature summary, the research results from the authors' group have been incor-
porated. In a subsection, different bioinert ceramics have been presented with
examples from the literature. The experimental results from the authors' group
on bioinert ceramics are also included and discussed elaborately. The next subsec-
tion describes the possibility of using glass-ceramic materials for orthopedic or
dental applications along with authors' recent research results. In some specifi c
implant applications, the importance of using bioinert material cannot be ignored.
Section 3.4 deals with polymeric biomaterials and their possible composites
in combination with other materials. In sections 3.4.1 and 3.4.2, the earlier works
on polymer-polymer and polymer-ceramic composite materials are discussed.
Section 3.5 critically assesses various examples of metallic biomaterials, as
well as the wear and corrosion properties of different metallic implants.
Section 3.6 deals with coating on metallic implants including their in vivo
functionality.
Finally, section 3.7 closes the chapter with an outlook on the present work
and the future perspective.
3.3 STRUCTURE AND PROPERTIES OF HARD TISSUES
As mentioned in the previous section, the focus of this review is on hard tissue
replacement materials and therefore, it is important, in the fi rst place, to discuss
the structure and properties of the natural hard tissues, that is, bone and teeth.
Based on its physical appearance, bone can be classifi ed as cancellous and cortical
bones. Cancellous bone (also called trabecular or spongy bone) has porous struc-
ture and behaves like an isotropic material under mechanical loading. On the
other hand, cortical bone has highly anisotropic microstructure, which leads to
higher strength in the direction of the loading axis 9 . Table 3.2 summarizes the
mechanical properties of bone and teeth.
Structurally, all hard tissues are formed from the four phases: collagen fi bers,
Ca-P rich mineral, organic substances, and water. The relative fractions of each
phase vary between bone types/teeth as well as on age/sex and anatomical loca-
tion within living body. Some related data for a typical cortical bone are included
in Table 3.3. In the case of teeth enamel, the mineral (HAp) content is as high as
95%. For the same reason, enamel is the hardest material in the human body.
Excluding organic mass and water, bone can be described as a natural nanocom-
posite, containing HAp nano-particles and collagen fi ber. The collagen fi bers pro-